There are a variety of hydrocarbon conversion processes, and these processes utilize different catalysts.
Alkylation is typically used to react light olefins, for example mixtures of alkenes such as propylene and butylene, with isobutane to produce a relatively high-octane branched-chain paraffinic hydrocarbon fuel, including isoheptane and isooctane. Similarly, an alkylation reaction can be performed using an aromatic compound such as benzene in place of the isobutane. When using benzene, the product resulting from the alkylation reaction is an alkylbenzene (e.g. cumene, linear alkylbenzenes, etc.).
The alkylation of paraffins with olefins for the production of alkylate for gasoline can use a variety of catalysts. The choice of catalyst depends on the end product a producer desires. Typical alkylation catalysts include concentrated sulfuric acid or hydrofluoric acid. However, sulfuric acid and hydrofluoric acid are hazardous and corrosive, and their use in industrial processes requires a variety of environmental controls. Sulfuric acid alkylation requires an often expensive regeneration process.
There has been a move to replace the use of sulfuric acid and hydrofluoric acid with more environmentally friendly materials.
One material that has been studied is ionic liquid. Ionic liquids are essentially salts in a liquid state, and are described in U.S. Pat. Nos. 4,764,440, 5,104,840, and 5,824,832. The properties vary extensively for different ionic liquids, and the use of ionic liquids depends on the properties of a given ionic liquid. Depending on the organic cation of the ionic liquid and the anion, the ionic liquid can have very different properties. Ionic liquids provide advantages over other catalysts, including possibly posing less of an environmental threat than catalysts like HF, and being non-volatile.
Processes utilizing ionic liquids as catalysts in hydrocarbon conversion processes, such as alkylation, isomerization, disproportionation, reverse disproportionation, and oligomerization have been developed.
In biphasic ionic liquid processes, such as alkylation, small droplets of ionic liquid become dispersed in the continuous hydrocarbon phase. Because ionic liquids are typically fairly expensive, the ionic liquid catalysts need to be recovered. Some recovery of the droplets of ionic liquid can be accomplished by gravity settling due to the density difference between the ionic liquid and the hydrocarbon, or other separation processes.
However, fine droplets of ionic liquid are difficult to be separated by gravity, and some remain dispersed in the hydrocarbon phase after these separation processes. These small droplets are carried out with the hydrocarbon. In addition to requiring post-treatments to prevent droplets from fouling down-stream equipment, they are an economic loss.
One process designed to separate the fine droplets of ionic liquid from the hydrocarbon is described in U.S. Pat. No. 8,067,656. A coalescer material having a stronger affinity for the ionic liquid than the hydrocarbons is used. The coalescer material can be a high surface area material having a large amount of contact area to which the dispersed ionic liquids can adhere. However, these materials may be prone to plugging due to fine openings or channels in the coalescence medium.
Therefore, there remains a need for processes and devices for recovering the dispersed fine droplets of liquid.